In the drive for higher integration and operating speeds in LSI devices, the pattern rule is made drastically finer. The rapid advance toward finer pattern rules is grounded on the development of a projection lens with an increased NA, a resist material with improved performance, and exposure light of a shorter wavelength. In particular, the change-over from i-line (365 nm) to shorter wavelength KrF laser (248 nm) brought about a significant innovation. Even mass fabrication of 0.18-μm rule devices becomes possible. To the demand for a resist material with a higher resolution and sensitivity, chemical amplification positive working resist materials which are catalyzed by acids generated upon light exposure are effective as disclosed in U.S. Pat. No. 4,491,628 and U.S. Pat. No. 5,310,619 (JP-B 2-27660 and JP-A 63-27829). They now become predominant resist materials especially adapted for deep UV lithography.
Resist materials adapted for KrF excimer lasers enjoyed early use on the 0.3 micron process, passed through the 0.25 micron rule, and currently entered the mass production phase on the 0.18 micron rule. Engineers have started investigation on the 0.15 micron rule, with the trend toward a finer pattern rule being accelerated. The change-over from KrF to shorter wavelength ArF excimer laser (193 nm) is expected to enable miniaturization of the design rule to 0.13 μm or less. Since conventionally used novolac resins and polyvinylphenol resins have very strong absorption in proximity to 193 nm, they cannot be used as the base resin for resists. To ensure transparency and dry etching resistance, some engineers investigated acrylic and alicyclic (typically cycloolefin) resins as disclosed in JP-A 9-73173, JP-A 10-10739, JP-A 9-230595 and WO 97/33198. With respect to F2 laser (157 nm) which is expected to enable further miniaturization to 0.10 μm or less, more difficulty arises in insuring transparency because it was found that acrylic resins are not transmissive to light at all and those cycloolefin resins having carbonyl bonds have strong absorption.
With respect to improvements in transmittance, it is reported that polymers having fluorine atoms and siloxane bonds have a relatively high transmittance. Various fluorine and silicon-containing polymers have been studied to develop resist compositions adapted for F2 laser. However, since fluorides and siloxanes are highly water repellent substances, there revealed a problem that such compositions were repellent to developers in the form of alkaline water. Because of a large contact angle with a developer, the developer did not spread over the entire surface of a wafer. Alternatively, because of poor penetration of the developer, development defects generated in that some space portions were not removed. Especially, the introduction of fluorine was effective for increasing transmittance, but was found to reduce developer wettability and dry etching resistance. The reduction of developer wettability is so significant that the resist film is repellent to the developer and prevents the developer from spreading over, or exposed areas are not dissolved, or a substantially insoluble surface layer causes the pattern profile to become T-top.
For resist compositions adapted for KrF and ArF exposure, methods of adding compounds containing water-soluble groups such as phenol, carboxyl, sulfonamide and carbonamide groups were proposed to solve the above problems. Examples include carboxylic anhydrides described in JP-A 2000-47385 and JP-A 2000-275840, phosphine compounds described in JP-A 2000-275838, thiocarbonyl group-containing compounds described in JP-A 2000-275841, carboxyl group-containing compounds described in JP-A 11-339150, and sulfonamide compounds described in JP-A 11-327145. However, all the foregoing substances exhibit strong absorption at 157 nm and thus have the drawback of reducing the transmittance of resist compositions.
There is a need to have an additive which is highly transparent and has good affinity to a developer.